Looking on the internet deeply has found these results:

I might not have been is the most popular phrase on the web.

I might have not been 136 results on the web	I might not have been 120,300,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I might not have been as happy as an expectant father should be. I might not have been able to save Roy... I mean, I might not have been paying that much attention, but... But I might not have even been watching you. If this had happened a couple of days ago, even yesterday, I might not have been so understanding. I might not have been very nice to you. You know, I might not have been able to... saveChristySuIIivan... butIdidn'teven try. I might not have been so lucky.	I mean, I might not have been paying that much attention, but... If this had happened a couple of days ago, even yesterday, I might not have been so understanding. I might not have been as happy as an expectant father should be. I might not have been so lucky. I might not have been very nice to you. I didn't, but I might not have been there alone. I might not have been completely straight with you, but I had good reason. I might not have been able to save Roy...

I might have not been

136 results on the web

I might not have been

120,300,000 results on the web

More popular!

I might not have been as happy as an expectant father should be.
I might not have been able to save Roy...
I mean, I might not have been paying that much attention, but...
But I might not have even been watching you.
If this had happened a couple of days ago, even yesterday, I might not have been so understanding.
I might not have been very nice to you.
You know, I might not have been able to... saveChristySuIIivan... butIdidn'teven try.
I might not have been so lucky.

I mean, I might not have been paying that much attention, but...
If this had happened a couple of days ago, even yesterday, I might not have been so understanding.
I might not have been as happy as an expectant father should be.
I might not have been so lucky.
I might not have been very nice to you.
I didn't, but I might not have been there alone.
I might not have been completely straight with you, but I had good reason.
I might not have been able to save Roy...